class_docstr: MRC Sample class to hold the mrc data info and provide atomic operations.
docstr: Get answer tokens start position and end position
docstr_tok: ["Get","answer","tokens","start","position","and","end","position"]
code: def get_answer_position(spans, answer_start, answer_end):
      r"""
      Get answer tokens start position and end position
  
      """
      answer_span = []
      for idx, span in enumerate(spans):
          if not (answer_end <= span[0] or answer_start >= span[1]):
              answer_span.append(idx)
      assert len(answer_span) > 0
      y1, y2 = answer_span[0], answer_span[-1]
      return y1, y2
  
imports: from .cnsample import CnSample
  from ..field import Field, CnTextField
  from ....common.utils.list_op import normalize_scope
  from ....common.preprocess.nltk_res_load import ModelManager
  from ....common.settings import *
  from nltk.stem.lancaster import LancasterStemmer
  from copy import deepcopy
label_desc: Use image node_id 19 for calling the MRCCnSample obj's underlying member method code with example usage: obj.get_answer_position(spans, answer_start, answer_end) and returns: y1,  y2